U.S. patent application number 12/514468 was filed with the patent office on 2010-06-24 for method and system to perform optical moving object detection and tracking over a wide area.
This patent application is currently assigned to VISIONMAP LTD.. Invention is credited to Michael Pechatnikov.
Application Number | 20100157055 12/514468 |
Document ID | / |
Family ID | 40341860 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157055 |
Kind Code |
A1 |
Pechatnikov; Michael |
June 24, 2010 |
METHOD AND SYSTEM TO PERFORM OPTICAL MOVING OBJECT DETECTION AND
TRACKING OVER A WIDE AREA
Abstract
A method for moving object detection, comprising generating a
time series of multi-exposures of scenes, each multi-exposure of a
scene comprising a sequence of at least two at least partially
overlapping images of that scene captured in rapid succession,
wherein the time series of multi-exposures periodically revisits
substantially the same scenes, detecting moving objects within each
multi-exposure by comparing its sequence of overlapping images, and
tracking objects by comparing moving objects detected within
multi-exposures of substantially the same scenes.
Inventors: |
Pechatnikov; Michael; (Tel
Aviv, IL) |
Correspondence
Address: |
DR. MARK M. FRIEDMAN;C/O BILL POLKINGHORN - DISCOVERY DISPATCH
9003 FLORIN WAY
UPPER MARLBORO
MD
20772
US
|
Assignee: |
VISIONMAP LTD.
Tel Aviv
IL
|
Family ID: |
40341860 |
Appl. No.: |
12/514468 |
Filed: |
August 7, 2008 |
PCT Filed: |
August 7, 2008 |
PCT NO: |
PCT/IL2008/001085 |
371 Date: |
May 12, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60954366 |
Aug 7, 2007 |
|
|
|
Current U.S.
Class: |
348/144 ;
348/E7.085; 382/103 |
Current CPC
Class: |
G06T 7/20 20130101; G06T
7/254 20170101; G06T 2207/30181 20130101; G06T 2207/30232
20130101 |
Class at
Publication: |
348/144 ;
382/103; 348/E07.085 |
International
Class: |
G06K 9/00 20060101
G06K009/00; H04N 7/18 20060101 H04N007/18 |
Claims
1. A method for moving object detection, comprising: generating a
time series of multi-exposures of scenes, each multi-exposure of a
scene comprising a sequence of at least two at least partially
overlapping images of that scene captured in rapid succession,
wherein the time series of multi-exposures periodically revisits
substantially the same scenes; detecting moving objects within each
multi-exposure by comparing its sequence of overlapping images; and
tracking objects by comparing moving objects detected within
multi-exposures of substantially the same scenes.
2. The method of claim 1 wherein said generating, said detecting is
performed within an airborne vehicle, the method further comprising
transmitting data characterizing the moving objects from the
airborne vehicle to a ground station.
3. The method of claim 2 wherein the data characterizing the moving
objects comprises, for each moving object, a capture time, object
location coordinates, an object velocity vector, and a thumbnail
image of the object.
4. The method of claim 1 wherein the at least two overlapping
images of the scene are captured within time intervals of 0.1-0.5
sec.
5. The method of claim 1 wherein the time series of multi-exposures
revisits the same scene with a revisit period of at least 5
sec.
6. The method of claim 1 wherein the multi-exposures are
double-exposures comprising two respective images captured by two
respective cameras.
7. The method of claim 1, wherein said detecting included detecting
at least one moving object not suspected to be in said each
multi-exposure prior to said detecting.
8. A moving object detection system, comprising: an airborne
segment, comprising: at least one camera for capturing images of
scenes; a moving object detector coupled with said at least one
camera, for receiving as input images of a scene, and for deriving
as output information about moving objects detected in the scene
and not suspected to be in the scene prior to being detected in the
scene; and an airborne controller coupled with said moving object
detector for receiving control commands from a ground segment, and
for controlling operation of said moving object detector in
response to the received commands; a ground segment comprising: an
object tracker for receiving as input information about moving
objects, and for deriving as output tracking information about the
moving objects; and a ground controller coupled with said object
tracker for issuing control commands to said airborne segment, and
for receiving information about moving objects from said airborne
segment in response to the control commands; and a communication
link for transmitting data between said airborne controller and
said ground controller.
9. The moving object detection system of claim 8, wherein said
airborne segment further comprises: an image compressor coupled
with said at least one camera, for compressing image data captured
by said at least one camera; and a data storage unit coupled with
said image compressor, for storing the compressed images generated
by said image compressor.
10. The moving object detection system of claim 8, wherein said at
least one camera captures a time series of multi-exposures M.sub.1,
M.sub.2, . . . , wherein each multi-exposure M.sub.k.sub.f of a
scene comprises a sequence, M.sub.k=(I.sub.k1, I.sub.k2, . . . ,
I.sub.km.sub.k), of at least two at least partially overlapping
images, I, of that scene, captured in rapid succession, wherein the
time series of multi-exposures periodically revisits substantially
the same scenes.
11. The moving object detection system of claim 10 wherein said at
least one camera captures successive images, I, of a
multi-exposure, M, at time intervals of approximately 0.2 sec.
12. The moving object detection system of claim 10 wherein the
scenes cover a large ground area, the size of which is controlled
via the revisit period.
13. The moving object detection system of claim 8 wherein said
communication link has a narrow bandwidth.
14. The moving object detection system of claim 8 wherein said at
least one camera has a ground sampling distance in accordance with
the sizes of objects that are tracked.
15. The moving object detection system of claim 8 wherein said
airborne segment travels at conventional velocities.
16. The moving object detection system of claim 8 wherein said
airborne segment travels at conventional altitudes.
17. A moving object detection system, comprising: an optical unit
comprising at least one camera for capturing images of scenes; an
airborne electronics unit comprising: a controller coupled with
said optical unit for controlling fields of view and image capture
times of said at least one camera, wherein said controller controls
said at least one camera to capture a time series of
multi-exposures of scenes, each multi-exposure of a scene
comprising a sequence of at least two at least partially
overlapping images of that scene captured in rapid succession,
wherein the time series of multi-exposures periodically revisits
substantially the same scenes; and a moving object detector coupled
with said optical unit for detecting moving objects within each
multi-exposure by comparing its sequence of overlapping images; and
a ground processing unit communicatively coupled with said first
electronics unit for tracking objects by comparing moving objects
detected within multi-exposures of substantially the same
scenes.
18. The moving object detection system of claim 17 further
comprising an airborne transmitter for transmitting data
characterizing the moving objects from the airborne vehicle to the
ground station via a communication link.
19. The moving object detection system of claim 18 wherein the data
characterizing the moving objects comprises, for each moving
object, a capture time, object location coordinates, an object
velocity vector, and a thumbnail image of the object.
20. The moving object detection system of claim 18 wherein said
airborne transmitter transmits data at low bit rate.
21. The moving object detection system of claim 17 wherein said
controller controls said at least one camera so as to capture the
at least two overlapping images of the scene within time intervals
of 0.1-0.5 sec.
22. The moving object detection system of claim 17 wherein said
controller controls said at least one camera so as to revisit the
same scene with a period of at least 5 sec.
23. The moving object detection system of claim 17 wherein said at
least one camera comprises two cameras, and wherein the
multi-exposures are double-exposures comprising two respective
images captured by said two respective cameras.
24. The moving object detection system of claim 17 wherein each of
said at least one camera is mounted rotatably on a gimbal.
25. The moving object detection system of claim 17 further
comprising means for controlling lines-of-sight of said at least
one camera.
26. The moving object detection system of claim 17 wherein said
moving object detector is for detecting moving objects not
suspected to be in said each multi-exposure prior to said
detecting.
27. A method for moving object detection, comprising: generating a
time series of multi-exposures of scenes, each multi-exposure of a
scene comprising a sequence of at least two at least partially
overlapping images of that scene captured in rapid succession,
wherein the time series of multi-exposures periodically revisits
substantially the same scenes; and detecting a moving object within
each multi-exposure by comparing its sequence of overlapping
images, said moving object not suspected to be in said each
multi-exposure prior to said detecting.
28. A moving object detection system, comprising: at least one
camera for capturing images of scenes; a moving object detector
coupled with said at least one camera, for receiving as input
images of a scene, and for deriving as output information about
moving objects detected in the scene and not suspected to be in the
scene prior to being detected in the scene; and an airborne
controller coupled with said moving object detector for receiving
control commands from a ground segment, and for controlling
operation of said moving object detector in response to the
received commands.
Description
PRIORITY REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional
Application No. 60/954,366, entitled METHOD AND SYSTEM TO PERFORM
OPTICAL MOVING TARGET AND CHANGE DETECTION INDICATION, filed on
Aug. 7, 2007 by inventor Michael Pechatnikov. This application is a
continuation-in-part of pending U.S. application Ser. No.
11/607,511 entitled DIGITAL MAPPING SYSTEM BASED ON CONTINUOUS
SCANNING LINE OF SIGHT, filed on Nov. 30, 2006.
FIELD OF THE INVENTION
[0002] The field of the subject invention is reconnaissance and
surveillance systems. More specifically, the subject invention
relates to wide area persistent monitoring systems.
BACKGROUND OF THE INVENTION
[0003] Moving object detection and change detection is a
well-researched field, with many applications in the security and
surveillance domain. Moving object and change detection systems are
required to provide automated, robust and real-time detection of
moving objects with a high probability of success and a minimal
rate of false alarms, without labor-intensive intervention.
[0004] Conventional moving object detection and tracking systems
are of two generic types; namely, real-time systems and off-line
systems. Real-time systems use static low-resolution video cameras,
typically HDTV or lower resolution. These video cameras track a
pre-designated area, typically limited in size due to the inherent
trade-off between field of view and ground sampling distance.
Real-time systems generally provide acceptable probabilities of
detection, but cover small areas; e.g., an area of 100 m.times.200
m at 10 cm resolution.
[0005] Off-line systems are used to detect changes over longer
periods of time and over wider areas than real-time systems.
Off-line systems typically operate by comparing satellite or other
aerial imagery over time periods ranging from several hours to
several months or even years. Off-line systems detect different
levels of change than do real-time systems, such as infrastructure
changes, which are largely irrelevant to real-time decision making.
In addition off-line systems lack robustness with respect to
viewing angle, lighting conditions, and other factors.
[0006] Robust motion detection generally requires capture of two
partially overlapping image frames with substantially similar
lighting conditions and perspective. Localization of moving objects
in two frames requires the revisit time to be sufficiently short,
e.g., less than 0.5 sec, in order to maintain close distances
between objects in both image frames. Revisit times that are too
short, e.g., less than 0.1 sec, may hide differences between two
frames, and prevent calculation of motion parameters. As such, a
desirable range for revisit times is 0.1-0.5 sec.
[0007] However continuous monitoring of a wide area is practically
impossible if a revisit time of 0.1-0.5 sec is to be maintained
over the entire area. Typically, revisit times for coverage of a
larger area are in the range of 5-120 sec.
[0008] There is currently no system that provides real-time moving
object detection over wide areas using optical sensors.
SUMMARY OF THE DESCRIPTION
[0009] Aspects of the subject invention provide novel methods and
systems for real-time object detection and tracking over wide areas
of coverage, by combining motion detection and estimation derived
from short revisit times with coverage of wide areas over longer
revisit times. The short revisit times correspond to a rapid
sequence of two or more at least partially overlapping images,
which is referred to herein as a "multi-exposure." For the case of
two images, the sequence is referred to herein as a "double
exposure".
[0010] In accordance with embodiments of the subject invention,
motion detection is performed on images of a multi-exposure.
Additionally, velocity estimation is performed on the images of the
multi-exposure, in order to localize objects in multi-exposures
that cover substantially the same area. The images of a
multi-exposure have substantially the same environmental
conditions, including inter alia angle of view and lighting. As
such, motion detection and velocity estimation based on
multi-exposures provide robust and reliable position and velocity
data, using simple real-time computational image processing.
[0011] Embodiments of the subject invention are able to monitor
small objects within wide areas, by mounting a camera and
processing assembly on board an aircraft, or such other airborne
vehicle including inter alia a balloon, a stratospheric airship and
an unmanned aerial vehicle (UAV).
[0012] The areas monitored by embodiments of the subject invention
are typically metropolitan areas. Images acquired of these areas
contain objects at different elevations, such as objects on roof
tops and objects on streets, with different perspective responses
to camera movement. Such differences generally result in
unacceptable levels of false alarms by conventional moving object
detection algorithms.
[0013] Tracking of moving objects in built-up metropolitan areas
requires short revisit periods. To capture high resolution images
over short revisit periods requires enormous capture rates and
pixel processing rates, in order to cover an area of interest. The
total amount of data collected is too large to be transmitted to a
ground station. As such, on-board processing is used, in order to
extract and transmit only essential moving object data.
[0014] Embodiments of the present invention apply to a wide
spectrum of signals. For ease of understanding, the present
description relates to UV, visible, near IR and IR signals. The
sensor device for these signals is referred to herein generically
as a "camera".
[0015] Embodiments of the present invention are of advantage in
many applications, including inter alia reconnaissance and
surveillance, traffic surveillance and law enforcement.
Reconnaissance and surveillance systems of the present invention
automatically detect, transmit and track moving objects in a wide
area, thus providing useful tactical information.
[0016] Traffic surveillance is performed by mounting systems of the
present invention inter alia on a balloon, on a UAV or on a
stratospheric airship. Such systems automatically provide useful
real-time traffic information, as well as information about illegal
driving and other traffic-related violations.
[0017] Law enforcement is performed by mounting systems of the
present invention inter alia on a balloon, on a UAV or on a
stratospheric airship. Such systems enable law enforcement agencies
to investigate events post-priori, and determine which vehicles or
persons arrived at a crime location, from where, and at what
time.
[0018] There is thus provided in accordance with an embodiment of
the subject invention a method for moving object detection,
including generating a time series of multi-exposures of scenes,
each multi-exposure of a scene including a sequence of at least two
at least partially overlapping images of that scene captured in
rapid succession, wherein the time series of multi-exposures
periodically revisits substantially the same scenes, detecting
moving objects within each multi-exposure by comparing its sequence
of overlapping images, and tracking objects by comparing moving
objects detected within multi-exposures of substantially the same
scenes.
[0019] There is additionally provided in accordance with an
embodiment of the present invention a moving object detection
system, including an airborne segment, including at least one
camera for capturing images of scenes, a moving object detector
coupled with the at least one camera, for receiving as input images
of a scene, and for deriving as output information about moving
objects detected in the scene, and an airborne controller coupled
with the moving object detector for receiving control commands from
a ground segment, and for controlling operation of the moving
object detector in response to the received commands, a ground
segment, including an object tracker for receiving as input
information about moving objects, and for deriving as output
tracking information about the moving objects, and a ground
controller coupled with the object tracker for issuing control
commands to the airborne segment, and for receiving information
about moving objects from the airborne segment in response to the
control commands, and a communication link for transmitting data
between the airborne controller and the ground controller.
[0020] There is further provided in accordance with an embodiment
of the subject invention a moving object detection system,
including an optical unit including at least one camera for
capturing images of scenes, an airborne electronics unit including
a controller coupled with the optical unit for controlling fields
of view and image capture times of the at least one camera, wherein
the controller controls the at least one camera to capture a time
series of multi-exposures of scenes, each multi-exposure of a scene
comprising a sequence of at least two at least partially
overlapping images of that scene captured in rapid succession,
wherein the time series of multi-exposures periodically revisits
substantially the same scenes, and a moving object detector coupled
with the optical unit for detecting moving objects within each
multi-exposure by comparing its sequence of overlapping images, and
a ground processing unit communicatively coupled with the first
electronics unit for tracking objects by comparing moving objects
detected within multi-exposures of substantially the same
scenes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The subject invention will be more fully understood and
appreciated from the following detailed description, taken in
conjunction with the drawings in which:
[0022] FIG. 1 is a simplified block diagram of a system for moving
object detection and tracking over a wide area, in accordance with
an embodiment of the present invention;
[0023] FIG. 2 is an illustration of a camera capturing images from
two fields of view in rapid succession, from an airborne segment in
flight, and the airborne segment transmitting derived moving object
data to a ground segment, in accordance with an embodiment of the
present invention; and
[0024] FIGS. 3A and 3B are illustrations of a rapid double-exposure
sequence of images captured by a camera corresponding to the fields
of view shown in FIG. 2, in accordance with an embodiment of the
present invention.
DETAILED DESCRIPTION
[0025] Embodiments of the subject invention concern methods and
systems for automated real-time moving object detection and
tracking over very wide areas using non-static cameras.
[0026] Reference is now made to FIG. 1, which is a simplified block
diagram of a system for moving object detection and tracking over a
wide area, in accordance with an embodiment of the present
invention. Shown in FIG. 1 is an airborne segment 100, which is
operative on board an aerial platform to capture images, to process
the captured images to detect moving objects, and to generate
moving object data. Counterpart to the airborne unit is a ground
segment 200, which is operative at a ground station to issue
mission commands and requests to airborne unit 100, to process
moving object data generated by airborne segment 100, and track the
moving objects.
[0027] Airborne segment 100 includes one or more cameras 110, and
RAM memory 120 for temporarily storing raw image data, an optional
JPEG2000 compressor 130 for compressing raw image data, or such
other image compressor, and an onboard storage unit 140 for storing
compressed image data. Airborne segment 100 also includes a moving
object detector 150, for processing image data to detect moving
objects within the images. Components of airborne segment 100 are
controlled by an airborne controller 160.
[0028] Ground segment 200 includes an object tracker 210, for
tracking objects detected by moving object detector 150. Ground
segment 200 also includes a tracking and image database 220 for
storing tracked object data, and a user interface 230 for
interactively accessing tracking and image database 220. Components
of ground segment 200 are controlled by a ground controller
240.
[0029] Airborne controller 140 and ground controller 240
communicate back and forth with one another via a communication
link 300. Airborne controller 140 receives mission planning
commands, and requests to onboard storage 140 from ground
controller 240. In response, airborne controller 140 transmits
moving object data generated by moving object detector 150, and
image data form onboard storage 140 to ground controller 240.
[0030] In an alternative embodiment of the subject invention,
communication link 300 is not used. Instead, data is stored on
board airborne segment 100 for off-line processing.
[0031] Prior art object detection and tracking systems use
two-dimensional imaging algorithms. Such systems do not perform
well with dynamic sensors, since differences in perspective cause
static objects to appear as moving. Generally, when images are
captured by non-static sensors, prior art systems have unacceptable
levels of false alarms.
[0032] In distinction, methods embodying the present invention use
photogrammetry and computer vision to reconstruct a
three-dimensional scene in real-time. These methods distinguish
between moving objects and static objects, even when sensor
movements cause perspective discrepancies in the images.
[0033] Methods embodying the present invention use photogrammetric
relative solve of images. Specifically, for substantially every
pixel in a source image, a corresponding epi-polar line is defined
in a destination image. Specific pixels in the destination image
are selected, and if a corresponding object in the source image is
not in its epi-polar line, or sufficiently far from an initial
estimate of its epi-polar line, then the object is deemed to be a
moving object. By using multi-exposures, taken over short time
intervals, the methods of the present invention perform
robustly.
[0034] Due to the short time spans between images in a
multi-exposure, the change of perspective between images is
relatively small. Consider, for example, an aircraft flying at an
altitude of H=2500 m, and at a speed of v=50 m/sec. Suppose the
onboard camera has a time span of t=0.2 sec between successive
images within a multi-exposure. For a building of height h=50 m,
the change in perspective of the building between successive images
is given by
P=h*t*v/H=0.2 m,
For a camera with a ground sampling distance of 10 cm/pixel, such
change in perspective corresponds to 2 pixels, which is relatively
small.
[0035] In one embodiment of the present invention, cameras 110
shown in FIG. 1 use mirror-based folding lenses to reduce the size
of an optical assembly while maintaining required focal lengths.
Mirror-based lenses require only simple motors for rotation.
Additional details regarding cameras 110 and their optical units
are described in applicant's co-pending application, U.S. Ser. No.
11/607,511 filed on Nov. 30, 2006, and entitled DIGITAL MAPPING
SYSTEM BASED ON CONTINUOUS SCANNING LINE OF SIGHT, the contents of
which are hereby incorporated herein by reference.
[0036] In accordance with an embodiment of the subject invention,
motion compensation is performed by tilting a mirror mounted on the
folding optics, using a piezoelectric tilt platform. Since the
weight and size of the mirror are small, motion compensation is
accurate.
[0037] It will be appreciated by those skilled in the art that
non-mirror based optics may alternatively be used in other
embodiments of the subject invention.
[0038] Further in accordance with embodiments of the present
invention, moving object detection is performed by acquiring a
rapid sequence of two or more images within a short time span, such
as a 0.1-0.5 sec. delay. The rapid sequence of images is referred
to herein as a multi-exposure. Partial overlap between images
enables motion detection. Notationally, the system of FIG. 1
captures successive a time series of multi-exposures M.sub.1,
M.sub.2, M.sub.3, . . . , where each multi-exposure, M.sub.k, is a
sequence of m.sub.k images
M.sub.k=(I.sub.k1, I.sub.k2, . . . , I.sub.k mk).
The multi-exposures are substantially periodic, with a revisit
period, p. I.e., over each time interval p the multi-exposures
capture substantially the same scenes. The images within each
multi-exposure are captured rapidly, typically within a delay
0.1-0.5 sec. between images, and the revisit period, p is generally
on the order of 5-120 sec.
[0039] Reference is now made to FIG. 2, which is an illustration of
a camera capturing images from two fields of view in rapid
succession, from airborne segment 100 in flight, and airborne
segment 100 transmitting derived moving object data to ground
segment 200, in accordance with an embodiment of the present
invention.
[0040] Reference is further made to FIGS. 3A and 3B, which are
illustrations of the rapid double-exposure sequence of images
captured by camera 110 corresponding to the fields of view shown in
FIG. 2, in accordance with an embodiment of the present
invention.
[0041] It will be appreciated by those skilled in the art that
embodiments of the present invention allow for trade-off of
coverage area and revisit period. The larger the coverage area, the
larger is the revisit period. Area of coverage is determined by the
flight path of an aircraft 400 transporting cameras 110, and by the
angles through which the camera gimbals swing. It will be
appreciated by those skilled in the art that other means may be
used instead to control the line-of-sight of cameras 110, in
accordance with other embodiments of the subject invention.
[0042] Using a gimbal controlled by controller 160, or such other
means to control the line-of-sight of cameras 110, the trade-off
between revisit period and coverage area is adjusted according to
an adaptable flight plan.
[0043] Accuracy of change estimation is determined by ground
sampling distance (GSD) and the delay time between image capture in
the multi-exposure sequence. E.g., if the GSD is 10 cm, and the
delay time between image frames is 0.2 sec, then objects moving at
1.8 km/h or faster are detectable.
[0044] Embodiments of the present invention perform real-time
tracking of objects. For tracking purposes, sampling of moving
objects is done with a revisit period generally between 5 sec and
120 sec per cycle. The revisit period is controlled by programming
a scan pattern to allow for frequent acquisition of multi-exposure
sequences. Generally, if an object is moving within one
multi-exposure, then it will be moving in the successive
multi-exposure as well. As such, tracking is performed by matching
of moving objects between two consecutive multi-exposures. When an
object starts or stops moving, it is searched for within a static
region of imagery.
[0045] In accordance with embodiments of the present invention,
wireless communication is used to transmit real-time data generated
within an airborne vehicle to a ground station. Since the pixel
collection rate of the systems is high, it is impractical to
transmit all of the image data to the ground station. Instead,
moving object detector 150 performs computer algorithms for moving
object detection onboard the aircraft. After the object motion
detection is computed onboard, only data about the moving objects
that are detected is sent to the ground station. The transmitted
data is organized in records, each record including an object
number, a thumbnail representation of the detected object, the
object's X, Y and azimuth coordinates, and the time of detection.
As such, the required bandwidth is reduced substantially.
[0046] A double-exposure sequence may be implemented in several
ways. In one implementation, two independently gimbaled cameras are
used, where the cameras substantially cover the same areas with
slight delays. In another implementation, two cameras are mounted
on the same gimbals with specific angles, so that the second camera
covers substantially the same areas as the first camera, with a
slight delay. In another implementation, a single camera is used,
the camera covering an area with a designated trajectory. In
another implementation, a single camera is used, which captures
several images per second and maintains significant overlap, such
as 50% overlap, between successive images.
[0047] Use of two cameras, as described hereinabove, enables
coverage of a larger area than one camera covers. In general, any
number of cameras may be used, as necessary for achieving specific
mission requirements.
[0048] It will be appreciated by those skilled in the art that
embodiments of the present invention afford several advantages over
prior art systems, including inter alia: [0049] 1. the ability to
automatically detect moving objects within densely built-up areas,
including inter alia people, and small vehicles; [0050] 2. the
ability to survey wide areas accurately; and [0051] 3. the ability
to detect objects moving at speeds ranging from 2 km/h to 140
km/h.
[0052] In distinction, for a representative revisit time of 5 sec,
prior art systems are typically able to monitor only 1/1000 of the
area that is monitored by embodiments of the present invention.
[0053] In the foregoing specification, the invention has been
described with reference to specific exemplary embodiments thereof.
It will, however, be evident that various modifications and changes
may be made to the specific exemplary embodiments without departing
from the broader spirit and scope of the invention as set forth in
the appended claims. Accordingly, the specification and drawings
are to be regarded in an illustrative rather than a restrictive
sense.
* * * * *